Previously, Japanese Unexamined Patent Application Publication No. 11-145704 has disclosed a multimode dielectric resonator device having a dielectric core disposed in a cavity and using a plurality of TM modes and TE modes.
In this multimode dielectric resonator device, when coupling is performed between predetermined modes by the shape of the dielectric core, perturbation on an electric field is performed by providing a groove or a hole at a portion on which electric fields to be coupled are concentrated in order to exchange energy between the resonance modes, thereby the coupling is performed.
However, in a known multimode dielectric resonator device, there has been a problem in that coupling is also produced between one TM mode and another TM mode at the same time even if the shape of the dielectric core is determined only by paying attention to the portion on which two modes of electric fields to be coupled are concentrated in order to perform the coupling between the TE mode and the TE mode.
For example, when coupling is performed between an TM01δ_x mode in which an electric field is rotated in a plane perpendicular to an x-axis and an TM01δ_y mode in which an electric field is rotated in a plane perpendicular to a y-axis in an x-y-z rectangular Cartesian coordinate system, a groove and a hole are provided at the portions through which the electric flux of an even mode and an odd mode, which are a coupling mode of both modes, pass in order to make a difference between the resonant frequencies of the even mode and the odd mode. Thereby, it is possible to couple the two TE modes described above with each other.
However, the groove and the hole described above cause perturbation to arise between an TM01δ-x mode in which an electric field is directed in an x direction and an TM01δ-y mode in which an electric field is directed in a y direction, and thus these two TM modes are coupled with each other. That is to say, in a multimode dielectric resonator using both the TM mode and the TE mode, when the coupling between the TE mode and the TE mode is performed, the coupling between the TM modes is also caused to arise, and thus it is difficult to independently determine the amount of coupling between the TE mode and the TE mode.
Also, if a dielectric core is provided with a groove or has a shape with a protruding part in order to perform coupling between the TE mode and the TE mode, the shape of the electric flux distribution is disarranged. As a result, the frequency of the basic mode increases or decreases. Thus, there has been a problem in that when a filter is constructed by coupling a plurality of resonant modes in sequence, the difficulty in adjusting the filter characteristics thereof increases.
Accordingly, an object of this invention is to provide a multimode dielectric resonator device which couples two TE modes, whose electric-field rotating planes have a perpendicular relationship, independently of the coupling between two TM modes whose electric-field directions have the same perpendicular relationships, respectively.
Also, another object of this invention is to couple the TE modes themselves while avoiding coupling of the TM modes having the relationship described above and to provide a multimode dielectric resonator device equipped with four-stage resonators of TM-mode-TE-mode-TE-mode-TM-mode by coupling the TM mode and the TE mode of the one side and coupling the TM mode and the TE mode of the other side, and furthermore another object of this invention is to provide a dielectric filter, a composite dielectric filter, and a communication apparatus including the above-described device.